Method and system for compensating for wheel wear on a train

ABSTRACT

A method and system for compensating for wheel wear uses position and/or speed information from an independent positioning system to measure some distance over which the train has traveled. Wheel rotation information is also collected over the distance. The wheel rotation information and distance and/or speed information are then used to determine the size of the train wheels. The method is performed periodically to correct for changes in wheel size over time due to wear so that the wheel rotation information can be used to determine train position and speed in the event of a positioning system failure.

This application is a U.S. Divisional application of U.S. applicationSer. No. 10/609,377, filed Jul. 1, 2003, which is a Continuation-In-Partof application Ser. No. 10/157,874, filed May 31, 2002, now U.S. Pat.No. 6,701,228, issued Mar. 2, 2004. The entirety of both of theabove-mentioned applications are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to railroads generally, and more particularly to asystem and method for determining wheel size to compensate for wheelwear.

2. Discussion of the Background

Controlling the movement of trains in a modern environment is a complexprocess. Collisions with other trains must be avoided and regulations inareas such as grade crossings must be complied with. The pressure toincrease the performance of rail systems, in terms of speed, reliabilityand safety, has led to many proposals to automate various aspects oftrain operation. For example, positive train control (PTC) and automatictrain control (ATC) systems have been widely discussed in recent years.

Some automated systems rely on global positioning system (GPS) receiversfor indications of train speed and position (as used herein, “globalpositioning system” and “GPS” refer to all varieties of globalpositioning system receivers, including, but not limited to,differential global positioning system receivers. Still other systemsuse inertial navigation systems (INSs) for determining speed andlocation. However, GPS receivers and INSs sometimes fail, and for thatreason it is desirable to have a back-up system.

One method that can be used in case of a positioning system failure isto measure the rotation of motor, axle or wheel rotation to determinethe speed at which a train is traveling and/or the distance which atrain has traveled. Each time the wheel makes a compete revolution, thedistance traveled by the wheel is equal to its circumference in theabsence of any slippage. Thus, if the radius R of the wheel is known,the distance traveled for each revolution of the wheel is equal to 2πR.However, the radius of a wheel changes over time due to wheel wear. Forexample, a standard train wheel can decrease in size from 40 inches to36 inches over its useful life. Therefore, the distance traveled in eachwheel revolution can vary between 125.7″ and 113.1″, a difference ofapproximately 12.6″ or 10%. This error is significant.

What is needed is a method and system that compensates for wheel wear.

SUMMARY OF THE INVENTION

The present invention meets the aforementioned need to a great extent byproviding a method and system for compensating for wheel wear in whichwheel rotation information from a revolution counter or a tachometer andposition and/or speed information from an independent positioning systemsuch as GPS or INS are measured over a predetermined distance and usedto determine the size of the train wheels. This process is performedperiodically to compensate for wheel wear.

In one aspect of the invention, the system includes a map database andthe position information from the independent positioning system is usedto as an index to ensure that the rotation data used for thespeed/position comparison between the position system and rotation datais collected in an area of straight and flat track so as to excludeerrors in the rotation data caused by wheel slippage and turns.

In another aspect of the invention, the data used for the comparisonbetween the speeds/distances indicated by the positioning system and bythe rotation data is collected over a long distance to minimize knownerrors in the positioning system. In yet another aspect of theinvention, a total distance traveled is calculated using an integrationtechnique by adding a plurality of linear differences in successivepositions reported by the positioning system over short periods of time.This technique is particularly advantageous when performed over curvedsections of track.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantfeatures and advantages thereof will be readily obtained as the samebecome better understood by reference to the following detaileddescription when considered in connection with the accompanyingdrawings, wherein:

FIG. 1 is a logical block diagram of a train control system according toone embodiment of the invention.

FIG. 2 is a flowchart showing a wheel wear compensation techniqueaccording to one embodiment of the invention.

FIG. 3 is a logical block diagram of a train speed signal distributionsystem according to another embodiment of the present invention.

FIGS. 4( a) and 4(b) are, respectively, schematic drawings of distancecalculated by a linear method and an integration method according to anembodiment of the present invention.

FIG. 5 is a flowchart of a wheel wear compensation technique employingthe integration method of FIG. 4( b) according to an embodiment of theinvention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention will be discussed with reference to preferredembodiments of train control systems. Specific details, such as wheelsizes and types of positioning systems, are set forth in order toprovide a thorough understanding of the present invention. The preferredembodiments and specific details discussed herein should not beunderstood to limit the invention.

Referring now to the drawings, wherein like reference numerals designateidentical or corresponding parts throughout the several views, FIG. 1 isa logical block diagram of a train control system 100 according to thepresent invention. The system 100 includes a control module 110, whichtypically, but not necessarily, includes a microprocessor. The controlmodule 110 is connected to a revolution counter 120. The revolutioncounter 120 measures rotation of a locomotive wheel (not shown inFIG. 1) on a train. The revolution counter 120 may be of any type,including mechanical, magnetic, and optical. The revolution counter 120may measure the rotation of a wheel directly, or may measure rotation ofan axle to which the wheel is connected, or may measure rotation of amotor driveshaft or gear that powers the wheel.

Also connected to the control module 110 is a positioning system such asa GPS receiver 130. The GPS 130 receiver can be of any type, including adifferential GPS receiver. Other types of positioning systems, such asinertial navigation systems (INSs) and Loran systems, can also be used.[As used herein, the term “positioning system” refers to the portion ofa positioning system that is commonly located on a mobile vehicle, whichmay or may not comprise the entire system. Thus, for example, inconnection with a global positioning system, the term “positioningsystem” as used herein refers to a GPS receiver and does not include thesatellites that are used to transmit information to the GPS receiver.]The GPS receiver 130 provides position and speed information to thecontrol module 110.

The control module 110 uses the position information from the GPSreceiver 130 as an index into a map database 140. The map database 140provides information including track grade and curvature to the controlmodule 110. As will be explained in further detail below, thisinformation is used in some embodiments to ensure that rotationinformation from the revolution counter will not include rotationinformation that is corrupted due to wheel slippage and/or errors due totrack curvature.

Referring now to FIG. 2, a flowchart 200 illustrates operation of awheel wear correction method according to one embodiment of the presentinvention. The control module 110 determines whether track conditionsare acceptable at step 210. In some embodiments, this is accomplished byobtaining the current position from the GPS receiver 130 and indexingthe map database 140 to determine the track grade and curvature over apredetermined length of upcoming track over which rotation informationis to be collected.

The predetermined length of track is preferably of a sufficient lengthsuch that any errors introduced by the inaccuracy of the globalpositioning system receiver 130 are minimized. Obviously, it isadvantageous to use as great a length as possible since the effect ofpositioning systems errors are decreased as the length is increased.However, there is a trade-off that must be made because if the length istoo great, the time required to complete the wheel correction algorithmis too long and/or the amount of curvature and grade in the tracksegment over which the data is to be taken preclude running thealgorithm over too much track in the system. In some embodiments, thepredetermined length of track is 100,000 meters. In such an embodiment,with a global positioning system having a position error on the order of30 meters, the total error is equal to (30+30)/100,000=0.0006=0.06%.

In the embodiment described by FIG. 2, the determination as to whethertrack conditions are acceptable is made at the start of the algorithm.In other embodiments, rotation data is only collected if the train istraveling greater than some minimum. The reason behind this is that mostwheel slippage occurs at slow speeds as a locomotive is attempting toaccelerate. Most locomotives use electric induction motors, and mostelectric motors used in locomotives have torque curves with torquesdecreasing as speed increases such that it is not possible for thelocomotive to generate enough torque to cause the wheels to slip abovecertain speeds. In some embodiments, the minimum speed at which datawill be collected is 15 m.p.h.; in other embodiments, the minimum speedis 20 m.p.h.

In yet other embodiments, the wheel acceleration is monitored to detectwheel slippage. If an acceleration exceeds a threshold, the collectedinformation is discarded and the entire process is started over.

In still other embodiments, the system notes the upcoming sections ofthe track in which either the grade or curvature is above acorresponding threshold and does not include those distances and anycorresponding rotation information collected over those distances in thecalculations. Such embodiments are particularly useful for railroads inwhich long, straight and level sections of track are not present in manyareas.

If the track conditions are not favorable at step 210, the system delaysfor a period of time at step 220 and repeats step 210 until trackconditions are favorable. When track conditions are favorable at step210, the control module 110 determines a start position from the globalpositioning receiver 130 at step 230 and counts rotations as measured bythe revolution counter 120 at step 240. When a threshold (which may be anumber of rotations and/or a time period) has been reached at step 250,the control module 110 determines a stop position from the globalpositioning receiver 130 at step 260. Next, at step 270, the controlmodule 130 calculates the distance D traveled based on the start andstop positions measured at steps 230 and 260, respectively. Then thecontrol module 130 determines the radius R of the wheel at step 280according to the equation R=D/2πT_(r), where T_(r) is the total numberof rotations counted over the distance D. The control module 110 thendelays, at step 290, for a period of time such as a day (it is notnecessary to run the algorithm often as train wheels wear slowly).

In the above-discussed embodiments, a predetermined distance is used. Itshould be noted that the predetermined distance will vary depending uponthe accuracy of the positioning system used and the particularenvironment in which the invention is used.

In the foregoing embodiments, data is not collected when the systemdetermines that track conditions are not favorable. However, in caseswhere curvature exceeds the threshold, it is also possible to allow datacollection to occur and correct the data for the curvature.

In another embodiment of the invention, an integration technique isutilized to correct for track curvature. In this technique, the totaldistance traveled is determined by adding linear differences betweenpositions reported by the positioning system at a plurality of shortintervals. In this manner, the sum of linear distances closelyapproximates the actual “track distance” (the actual distance traveledby the train over the track). Consider the examples shown in FIGS. 4( a)and 4(b), which illustrate a section of track 400 between two points Aand B. In FIG. 4( a), a linear distance D_(o) between points A and B isillustrated. This distance D_(o) is obviously less than the actual trackdistance between points A and B. In FIG. 4( b), several linear distancesD₁₋₉ between a plurality of intermediate points I₀₋₉ are calculated. Thesum of these linear distances D₁₋₉ is a much closer approximation of thetrack distance between points A and B. As the distance between theintermediate points I₀₋₉ decreases, the approximation of the actualtrack distance becomes more accurate.

FIG. 5 illustrates a flow chart 500 of the steps performed by thecontrol module 110 in an embodiment employing this integrationtechnique. The revolution counter 120 is reset to zero at step 502 (inother embodiments, the revolution counter is simply read at step 502).The position is then obtained from the positioning system 130 at step504 and temporarily stored as the last position at step 506. The controlmodule 110 then delays for a period of time at step 508. As discussedabove, the shorter the period is, the more accurate the approximationwill be. In preferred embodiments, the period is one second.

After the delay at step 508, the control module 110 again obtains thecurrent position at step 510. Next, the linear difference between thecurrent position and the temporarily stored last position is calculatedat step 512 and the difference is added to a total distance at step 514.

If the total distance does not exceed a threshold at step 516, steps 506et seq. are repeated. As discussed above, the selection of the thresholdinvolves a tradeoff. Again, a threshold of 100,000 meters is used insome embodiments.

If the threshold is exceeded at step 516, the revolution counter is readat step 518. The wheel circumference is then calculated by dividing thetotal distance by the number of revolutions from the revolution counter120.

In the embodiment described above, the periods of time during which thetotal distance was traveled were contiguous such that one period beganas soon as a previous period ended. This simplified the method byeliminating the necessity of reading the revolution counter at thebeginning and end of each period. Those of skill in the art willrecognize that it is not necessary for the periods to be contiguous andthat the invention may also be practiced by using a plurality ofnon-contiguous periods and reading the revolution counter at thebeginning and end of each period (or, alternatively, resetting therevolution counter at the beginning of each period).

In the foregoing embodiments, positional inputs from the positioningsystem are used; however, it will be readily apparent that speed canalso be used. For example, if the current speed S of the train is knownfrom the positioning system, then the wheel size can be determinedaccording to the equation S=DF_(r)=2πRF_(r), where D is the distancetraveled in each rotation, F_(r) is the rotation frequency of the wheel,and R is the radius of the wheel. In practice, the speed from the globalpositioning system may be read a number of times and the wheel sizecorresponding to each reading may be averaged. It should be noted thatusing speed rather than position information allows the wheel size to bedetermined more rapidly than using position information and is thereforepreferable when wheel size is needed quickly (such as when a gross errorhas been detected). However, using position information, especially overa long distance, results in greater accuracy. Accordingly, in someembodiments, speed is used to rapidly generate an initial estimate andposition is used to generate a better estimate at a later time.

Furthermore, while track curvature and grade were determined byreferencing a map database in the embodiments discussed above, it willbe readily recognized by those of skill in the art that curvature andgrade can be determined from altitude and direction information providedby the global positioning system. For example, the track curvature maybe determined by recording the train's position as reported by thepositioning system at several times during the period in which data iscollected. This position information can be used to construct acurvature profile so that the amount of curvature can be determinedafter the data is collected. If the curvature is greater than athreshold, the data can be ignored, or, in some embodiments, can becorrected for the curvature such as by using the integration techniquediscussed herein. The same techniques can be used to construct a gradeprofile.

It should also be noted that the invention may be incorporated intovarious types of train control systems, including the aforementioned PTCand ATC systems as well as many others.

In another embodiment of the invention, the wheel wear compensationmethod is incorporated into a wheel revolution sensor signaldistribution/conversion system such as the QUIP™ system manufactured bythe assignee of the present invention, Quantum Engineering. There may beseveral systems on board a train that input a signal representative ofthe wheel rotation and use that signal to calculate speed. For example,many locomotives that have been retrofitted with a train control systemalso are equipped with a separate speed display. Such systems typicallyrequire the conductor/engineer or maintenance personnel to measure thediameter of the train wheel to which the wheel sensor is attached andset DIP switches or otherwise configure the devices to indicate thewheel size. Because the wheel size changes over time as discussed above,these other devices must be reconfigured on some periodic basis, therebyincreasing labor costs.

Because there may be several systems that require the wheel sensorsignal which together constitute a larger electrical load than the wheelsensor is capable of handling, and because some of these systems requirean input signal of a different form than is supplied by the wheelsensor, signal conversion/distribution systems such as theaforementioned QUIP™ distribution/conversion system have been devised. Asubstantial savings can be realized by modifying thesedistribution/conversion systems to output a modified signal that isrepresentative of a wheel sensor signal would be generated by a wheel ofa fixed size. Thus, for example, if the conversion/distribution systemoutputs a modified wheel sensor signal that is representative of a 40inch wheel, each of the other systems that use the wheel sensor signalcould be configured once for a 40 inch wheel and would thereafter notneed to be periodically reconfigured.

Such a conversion/distribution system 300 is illustrated in FIG. 3. Thesystem includes a control unit 110 connected to a wheel revolutionsensor 320. In some embodiments, the wheel sensor 320 outputs a squarewave, with each rising edge representing a revolution of the wheel.Thus, the time between leading edges represents the time taken for onefull revolution of the wheel. It will be readily understood that thesignal output by the wheel sensor 320 may be of many forms, analog ordigital, and that the particular form of the signal is not important.Also connected to the control unit 110 is a GPS receiver 130 and a mapdatabase 140. The control unit 110 is configured to determine the wheelsize using the method described in FIG. 2 or one of the other methodsdescribed herein. The control unit 110 determines the speed of thetrain, which can be taken from the GPS receiver 130 or can be determinedwith the knowledge of the previously determined wheel size. Using theactual speed of the train, the control unit 110 then determines theparameters necessary for a signal that would be representative of thesignal that would be generated by the wheel sensor 320 if the wheel werea predetermined size such as 40″. For example, where the wheel sensoroutputs a square wave signal as discussed above, the period of thesquare wave when the train is traveling 30 m.p.h. would be the distancetraveled by one revolution, 2*π*20 inches, divided by the train speed,30 m.p.h. or 528 inches/sec, which is equal to 125.7/528=0.238 seconds.This 0.238 second period is supplied by the control unit 110 to a signalgenerator 180, which generates a square wave of the type discussed abovewith a period of 0.238 seconds. The signal generated by the signalgenerator 180 is then supplied to other systems A, B and C 191-193.Because the signal output by signal generator 180 will always berepresentative of a 40 inch wheel, it is not necessary to reconfigurethe other systems 191-193 once they have been configured for a 40 inchwheel, thereby substantially reducing labor costs associated with theseoperations.

In the embodiment discussed above, speed is determined as part of theprocess of determining the parameters of the signal to be generated bythe signal generator 180. It will be readily apparent to those of skillin the art that the parameters can be determined without actuallycalculating the speed. For example, once the wheel size is determinedusing the method of FIG. 2, that wheel size can be used to form a ratioof the predetermined wheel size to the actual wheel size. Thus, forexample, if the predetermined wheel size is 40 inches, and the actualwheel size is 36, the ratio would be 40/36. The control unit can thenmeasure the period of the square wave and multiply the period by theratio to determine the period of the signal that would be generated bythe wheel sensor 320 if the wheel were actually 40 inches, and supplythis period to the signal generator 180 to generate this signal.

As discussed above, it is possible to generate a signal for the otherdevices without using the signal from the wheel sensor 320. That is, thespeed can be determined from the positional system (e.g., GPS receiver130) and the parameters of the desired signal can be sent to the signalgenerator so that a signal can be generated and distributed to the othersystems, all without an actual wheel rotation sensor 320. This allowsthe system to serve as a back up for situations where the wheel sensorfails. This also allows the wheel sensor to be replaced, but such asystem has the drawback that it will not provide a correct signal whenthe GPS system is not operational.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

1. A method for supplying a signal to a device configured to process awheel sensor signal from a wheel sensor connected to a wheel of apredetermined size comprising the steps of: determining a speed of atrain without the use of a wheel sensor connected to a wheel of thepredetermined size; determining a parameter of a signal indicative of aspeed of the train that would be output by a wheel sensor connected to awheel of a predetermined size if the wheel were rotating at a ratecorresponding to the speed of the train; generating a wheel sensorsignal having the parameter; supplying the wheel sensor signal to atleast one device configured to process a wheel sensor signalcorresponding to a wheel sensor connected to a wheel of thepredetermined size.
 2. The method of claim 1, wherein the speed of thetrain is obtained using a positioning system.
 3. The method of claim 2,wherein the positioning system is configured to supply a speed.
 4. Themethod of claim 3, wherein the speed of the train is determined by:obtaining a first position from the positioning system at a first time;obtaining a second position from the positioning system at a secondtime; calculating a linear distance between the first and secondpositions; calculating an elapsed time between the first and secondtimes; calculating a speed of the train based on the linear distancebetween the first and second positions and the elapsed time between thefirst and second times.
 5. The method of claim 4, wherein a plurality oflinear distances are calculated for a plurality of positions reported bythe positioning system and the speed is based on the plurality of lineardistances and a plurality of corresponding elapsed times.
 6. The methodof claim 5, further comprising the steps of: determining a total numberof wheel revolutions occurring during each of the elapsed times for awheel sensor configured to measure a rotation of a wheel on the train;and calculating a wheel size based on the total number of wheelrevolutions, a total of the plurality of linear distances and a totalelapsed time.
 7. The method of claim 6, wherein the wheel size is usedto determine the speed of the train.
 8. The method of claim 4, furthercomprising the step of: determining a total number of wheel revolutionsduring the elapsed time from a wheel sensor configured to measure arotation of a wheel on the train; and calculating a wheel size based onthe total number of revolutions, the elapsed time and the lineardistance.
 9. A system for supplying a signal to a device configured toprocess a wheel sensor signal from a wheel sensor connected to a wheelof a predetermined size, the system comprising: a control unit; and asignal generator connected to the control unit; wherein the control unitis configured to perform the steps of: determining a speed of a vehicleon which the control unit is located without use of a wheel sensorconnected to a wheel of the predetermined size; determining a parameterof a signal that would be output by a wheel sensor connected to a wheelof a predetermined size if the wheel were rotating at a ratecorresponding to the speed; and controlling the signal generator togenerate a wheel sensor signal having the parameter; wherein the wheelsensor signal is output to a device configured to process a wheel sensorsignal from a wheel sensor associated with a wheel of the predeterminedsize.
 10. The system of claim 9, further comprising a positioning systemconnected to the control unit, wherein the speed of the train isdetermined from a message from the positioning system.
 11. The system ofclaim 10, wherein the positioning system is configured to indicate aspeed in the message.
 12. The system of claim 10, wherein the controlunit is configured to determine the speed of the train by performing thesteps of: obtaining a first position from the positioning system at afirst time; obtaining a second position from the positioning system at asecond time; calculating a linear distance between the first and secondpositions; calculating an elapsed time between the first and secondtimes; calculating a speed of the train based on the linear distancebetween the first and second positions and the elapsed time between thefirst and second times.
 13. The system of claim 12, wherein a pluralityof linear distances are calculated for a plurality of positions reportedby the positioning system and the speed is based on the plurality oflinear distances and a plurality of corresponding elapsed times.
 14. Thesystem of claim 13, wherein the control unit is further configured toperform the steps of: determining a total number of wheel revolutionsoccurring during each of the elapsed times for a wheel sensor configuredto measure a rotation of a wheel on the train; and calculating a wheelsize based on the total number of wheel revolutions, a total of theplurality of linear distances and a total elapsed time.
 15. The systemof claim 14, wherein the wheel size is used to determine the speed ofthe train.
 16. The system of claim 12, wherein the control unit isfurther configured to perform the steps of: determining a total numberof wheel revolutions during the elapsed time from a wheel sensorconfigured to measure a rotation of a wheel on the train; andcalculating a wheel size based on the total number of revolutions, theelapsed time and the linear distance.